It's a Gnarley One! (Gn1)
--Toshi Foster and Sarah Hake

Gnarley 1 (Gn1) is a new dominant mutation that was recovered by Dr. Tony Pryor at CSIRO, Australia. The mutation arose spontaneously as a single plant in a control population of a transposon tagging experiment, specifically, a family selected for the absence of active Ac at the P locus.

The Gn1 phenotype is characterized by reduced internodal length, a sinuously curving culm (Fig. 1), lack of a distinct boundary between blade and sheath, and extra silks that originate from the base of mature carpels. The position of the extra silks suggests that they are transformed stamens. The mutation is evident in young seedlings, affects all nodes, and is fully penetrant in several backgrounds. We mapped the Gn1 mutation to 2L using waxy reciprocal translocation stocks.

The Gn1 phenotype is reminiscent of the Knotted1 and Rough Sheath1 phenotypes in the disturbance of the ligule region and the twisted stature. Since both Kn1 (Vollbrecht et al., Nature 350:241-243) and Rs1 (Freeling, Dev. Bio. 153:44-58) encode homeodomains, we speculated that Gn1 may also fall in this class of homeobox-containing genes. Using the kn1 homeobox as a low stringency hybridization probe, members of the Hake laboratory have isolated approximately 12 additional homeobox genes which have been designated knox for knotted like homeobox. The clones were mapped using Recombinant Inbred populations and one of them, knox4, was shown to map to 2L within one map unit of bnl17.19b at 2L162. When we used knox4 as a probe on a Southern of a segregating population of 52 Gn1 and 64 normal plants, we found only one recombinant, which was possibly misidentified as normal. Preliminary northern data indicates that knox4 hybridizes to a transcript of about 1.6 kb. knox4 is highly expressed in both normal and Gn1 vegetative and ear meristems, is absent from normal leaves and is ectopically expressed in Gn1 leaves. knox4 is not ectopically expressed in Kn1 mutant leaves, nor is kn1 ectopically expressed in Gn1 mutant leaves. These observations strongly support the hypothesis that knox4 corresponds to Gn1. In situ analysis with knox4 is in progress to determine which tissues or cells are ectopically expressing knox4. In order to prove that Gn1 is a mutation of the knox4 gene, we are trying to knock out the dominant phenotype with transposon insertions.
 

Figure 1. Photograph of the Gnarley1 mutation courtesy of Dr. Tony Pryor.

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